Buncombe County, NC Accessory Structures: ADU Rules (2026)

Buncombe County's zoning is governed by Chapter 78 of the Code of Ordinances (Municode). The county's residential and open-use districts each list 'two residential dwelling units (attached or detached)' among their permitted uses by right: R-LD Low-Density Residential, R-1 Residential (single- and two-family), R-2 Residential, R-3 Residential (which also allows multifamily where utilities are available), and the OU Open Use district where most uses are allowed by right. This means a property owner in unincorporated Buncombe County can typically build a second home or a detached accessory dwelling on the same lot without a special use permit, as long as both units satisfy the lot-size and setback rules in §78-642 (dimensional requirements) for the underlying district. Section 78-662 caps a single lot at four principal buildings plus customary accessory buildings, with exceptions for planned unit developments and places of worship. When an ADU is built as a detached accessory structure, §78-663 controls placement: smaller accessory buildings (320 square feet or less and 15 feet tall or less) require 7-foot side and rear setbacks, while larger accessory structures (more than 320 sf or taller than 15 ft) need 7-10 foot side setbacks (depending on whether public sewer is available) and a 10-foot rear setback; front setbacks follow the underlying district. If the existing primary structure is legally nonconforming on front setbacks, accessory buildings may match that line. Accessory uses cannot include any use that is otherwise prohibited or that would itself require a special use permit. Travel trailers and recreational vehicles cannot serve as ADUs in residential districts. On top of these local rules, North Carolina Session Law S495 (2025-2026 session, applicable to permit applications submitted on or after October 1, 2025) requires every local government to allow at least one ADU that conforms to the NC Residential Code per single-family detached dwelling in residential zones, prohibits parking minimums tied to the ADU, and bars maximum unit sizes below 800 square feet; local governments must adopt conforming regulations by January 1, 2027 or ADUs default to no local limitations. Buncombe County's existing 'two-units-by-right' framework already meets the core S495 mandate. Building permits, zoning permits, and septic/health-department approval (where public sewer is unavailable) are issued by the Buncombe County Planning & Development Department; the City of Asheville, Town of Black Mountain, and other municipalities have their own zoning ordinances that are not covered by Chapter 78.